Fabrication of computer circuitry of increasingly smaller size has been one of the driving forces in the development of computers since their inception. Laptop computers available today have higher processing speeds and more power than a computer which filled an entire room in the late 1940's and early 1950's.
The demand for more powerful and smaller computers for a multitude of applications will continue to spur the computer industry to reduce the size of computers and their components. Also, with the development of increasingly more powerful, faster and more complex computers, the need to limit propagation delays caused by the distance a signal must travel between components of a computer system will become of more concern to the industry. In the near future, propagation distances of several centimeters between components of a computer system may create limits to the operation of a computer system which can only be resolved by further reductions in size.
Bonding of multiple stacked semiconductor chips together into a module is one method under development to reduce the physical area taken up by a computer and its circuitry and to reduce propagation delays. The module of bonded chips, sometimes referred to as a "cube," usually takes the form of a right parallelpiped. The chips as bonded together in the module have connectors distributed on one face of the module to connect the module to a base or carrier, both physically and electrically.
The high chip density of such modules present other problems. One of the primary problems to be resolved is the elimination of the excess heat generated by operation of the chips in such close proximity in the module.
The temperature range over which a silicon chip, fabricated by present day methods, can operate in a fairly safe manner is from 20.degree. to 120.degree. C. However, given the power consumption of many of these chip modules, temperatures of the module can easily exceed the 120.degree. C. limit of a silicon chip if not properly cooled. Moreover, silicon chips operate most effectively and efficiently in a temperature range of from 20.degree. to 40.degree. C. Similarly, the temperature of a module made up of chips of gallium arsenide can easily exceed 170.degree. C., the safe operating limit of gallium arsenide chips.
Failure to properly control the temperature of a module can result in degradation of, and destruction of, the electronic circutry devices on the chips. Excessive heat can also affect the efficiency of operation, even if it does not result in outright destruction of the components of the chips. Thermal expansion of the module and chips, although not of a sizable amount, can also cause serious harm and damage to the module and chips which form the structure of the module if not properly controlled.
Thermal analysis of the operation of semiconductor chips indicates that the temperature difference between the center of the chip and its edge will by only a few degrees and that the chip itself can transmit temperature difference from its center to its edges in a fairly efficient manner. Thus, the challenge is to adequately cool the chips when combined in a module to maintain an operational temperature within the most effective and safe ranges for chips of the module.